HPLC is the most powerful technique available for peptide separation. However, the usefulness of HPLC for peptide measurement has been limited by the poor sensitivity of detection with UV monitors operating at 210 nm. Twenty compounds were tested for ability to rapidly form "clean" derivatives of peptides which could be detected with high sensitivity by absorbance or electrochemical detectors. Two compounds were synthesized which react rapidly (T 1/2 less than 1 min) with amino groups of peptides forming hydrophilic derivatives with a 50-500 fold improvement in detection limits over conventional methods. An arylating agent, 2 carboxy, 4,6 dinitrofluorobenzene (CDNFB) allows detection of 10 pmol of a dipeptide by absorbance at 360nm in comparison to the 500 pmol limit of the underivatized dipeptide at 210nm. An acylating agent, 3,6-dinitro phthalic anhydride forms a hydrophilic peptide derivative which can be detected electrochemically by reduction at -0.3 V at the 1 pmol level.